The long-term goal is to gain greater understanding of the role of the human and subhuman primate fetal gonad in sexual development. As an intermediate step leading to this goal, a series of in vitro and in vivo studies are planned. In vitro, it is proposed to study: 1) factors influencing growth of the fetal gonad by assessing the effects of epidermal growth factor, fibroblast growth factor, serum and placental extract on gonadal cell proliferation; 2) binding of gonadotropins to the fetal gonads and correlation of this binding with functional activity of the gonads; 3) facets of hCG formation by the human fetus, including synthesis by the fetal gonad, binding to fetal thyroid membranes and separation of fetal from placental hCG; and 4) possible factors responsible for the apparent lack of desensitization of fetal leydig cells by hCG. In vivo, in the long-term catheterized rhesus monkey fetus, it is proposed to determine: 1) whether there is pulsatile discharge of LH and FSH; 2) the effects of pulsatile administration of gonadotropin-releasing hormone on gonadotropin and gonadal steroid production; and 3) the possible modulating effects of opiate peptides and other modulators on gonadotropin production. As gonadal function, at least of the testis, is necessary for normal sexual development, and as gonadotropin-gonadal interactions differ significantly between primates and other experimental animals, greater understanding of these phenomena in the primate has significant biomedical relevance.